The Carbon Emissions Reduction Target (CERT) - which came into effect on 1 April 2008 and ran until December 2012 - was an obligation on energy suppliers to achieve targets for promoting reductions in carbon emissions in the household sector. It was the principal driver of energy efficiency improvements in existing homes in Great Britain over the period. It doubled the level of activity of its predecessor Energy Efficiency Commitment (EEC) to deliver overall lifetime savings of 154 MtCO2. In September 2008 the government increased the CERT target by 20%, increasing the scheme's lifetime carbon savings to 185 MtCO2. (31 MtCO2 more than under the original CERT target of 154 MtCO2). In addition to the energy efficiency measures of the current EEC, suppliers will be able to promote microgeneration measures; biomass community heating and CHP; and other measures for reducing the consumption of supplied energy. Suppliers had to direct at least 40% of carbon savings to a priority group of low-income and elderly consumers. Extending the priority group to include the over-70s ensured that a large number of fuel poor households, who are not eligible under the current criteria, become eligible for support. CERT ended in December 2012, replaced by the Energy Company Obligation and the Green Deal.